FreeRTOS学习-02-读懂汇编代码

野性酷女 2023-07-03 10:49 5阅读 0赞

FreeRTOS中有少量的内联汇编代码，并不复杂。

准备一些手册，搜索关键字就可以很快的找到有用的信息。

1.准备一些手册

ELF for the Arm Architecture

ARM v7-M Architecture Reference Manual

User Manual The GNU Assembler

GNU ld manual：

[http://ftp.gnu.org/old-gnu/Manuals/ld-2.9.1/html\_mono/ld.html][http_ftp.gnu.org_old-gnu_Manuals_ld-2.9.1_html_mono_ld.html]

[https://sourceware.org/binutils/docs/ld/][https_sourceware.org_binutils_docs_ld]

所有GNU的手册：

[http://www.gnu.org/manual/][http_www.gnu.org_manual]

2.利用手册去读懂startup.s

startup.s要配合ld script文件一起读，可能还需要先读一下ELF for the Arm Architecture

/\*注释的目的是看懂，之后在freertos里也有一些汇编代码\*/  
.syntax unified  
.cpu cortex-m3  
.fpu softvfp  
.thumb

/\*irq vector table and default handler\*/  
.global g\_pfnVectors  
.global Default\_Handler

/\* 指示data bss段的起始位置,赋值在ld script文件中\*/  
/\* start address for the initialization values of the .data section.  
defined in linker script \*/  
/\*\_sidata要结合ld scatter/script文件来确定，实际上存储了data段在flash中的地址\*/  
.word \_sidata  
/\* start address for the .data section. defined in linker script \*/  
.word \_sdata  
/\* end address for the .data section. defined in linker script \*/  
.word \_edata  
/\* start address for the .bss section. defined in linker script \*/  
.word \_sbss  
/\* end address for the .bss section. defined in linker script \*/  
.word \_ebss

/\*BootRAM的值是0xF108F85F\*/  
.equ BootRAM, 0xF108F85F  
/\*\*  
\* @brief This is the code that gets called when the processor first  
\* starts execution following a reset event. Only the absolutely  
\* necessary set is performed, after which the application  
\* supplied main() routine is called.  
\* @param None  
\* @retval : None  
\*/  
/\*这个text.Reset\_Handler很有迷惑性，它就是一个段名，在ld script中有 \*(.text\*)\*/  
.section .text.Reset\_Handler  
/\*.weak 如果这个符号名没有被定义，那么就创建它\*/  
/\*在quick referance没有的，要到GNU AS Manual搜索\*/  
.weak Reset\_Handler  
/\*设置Reset\_Handler符号的类型为函数,也就是说Reset\_Handler是函数的名字\*/  
.type Reset\_Handler, %function  
/\*.section定义了Reset\_Handler所属的段，.weak和type定义了它的属性\*/  
Reset\_Handler:

/\* Copy the data segment initializers from flash to SRAM \*/  
/\*汇编指令的语法和功能要参考对应的指令集,简单的就不再注释\*/  
/\*这段代码是未后面的代码完成必要的初始化工作，所以并没有出现压栈和出栈操作\*/  
movs r1, \#0 /\*r1=0,r1是传递给LoopCopyDataInit的一个参数，可以查询APCS\*/  
b LoopCopyDataInit /\*b即branch,所以接下来跳转到LoopCopyDataInit标号执行\*/

CopyDataInit:  
ldr r3, =\_sidata /\* r3 = \_sidata \*/  
ldr r3, \[r3, r1\] /\* r3 = \*(r3 + r1) \*/  
str r3, \[r0, r1\] /\* \*(r0 + r1) = r3 \*/  
adds r1, r1, \#4 /\* r1 += 4 \*/  
/\*程序继续执行LoopCopyDataInit\*/

LoopCopyDataInit:  
/\*这里就是一个for循环初始化data段\*/  
ldr r0, =\_sdata /\*ldr是伪指令,armV7指令集查不到，要在arm asm的手册查\*/  
ldr r3, =\_edata /\*r0 = \_sdata; r3 = \_edata;\*/  
adds r2, r0, r1 /\*r2 = r0 + r1;并更新标志位\*/  
cmp r2, r3 /\*根据r2 - r3的结果更新标志位\*/  
bcc CopyDataInit /\*b是跳转cc是条件，r2 >= r3\*/  
ldr r2, =\_sbss /\*初始化完data段，开始初始化bss段\*/  
b LoopFillZerobss  
/\* Zero fill the bss segment. \*/  
FillZerobss:  
movs r3, \#0  
str r3, \[r2\], \#4

/\*也是一个for循环，和前面的功能类似，只不过bss段不从flash加载，直接初始化为0\*/  
LoopFillZerobss:  
ldr r3, = \_ebss  
cmp r2, r3  
bcc FillZerobss

/\* Call the clock system intitialization function.\*/  
bl SystemInit /\*跳转到时钟初始化的函数,bl和b不同的地方是会做lr=pc操作\*/  
/\* Call static constructors \*/  
bl \_\_libc\_init\_array /\*初始化必要的对象\*/  
/\* Call the application's entry point.\*/  
bl main /\*跳转到main()函数,一般就不会返回了\*/  
bx lr  
.size Reset\_Handler, .-Reset\_Handler /\* 指定Reset\_Handler的大小\*/

/\*\*  
\* @brief This is the code that gets called when the processor receives an  
\* unexpected interrupt. This simply enters an infinite loop, preserving  
\* the system state for examination by a debugger.  
\*  
\* @param None  
\* @retval : None  
\*/  
/\*progbits手册查到含义是段包含数据\*/  
.section .text.Default\_Handler,"ax",%progbits  
Default\_Handler:  
/\*死循环\*/  
Infinite\_Loop:  
b Infinite\_Loop  
.size Default\_Handler, .-Default\_Handler  
/\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*  
\*  
\* The minimal vector table for a Cortex M3. Note that the proper constructs  
\* must be placed on this to ensure that it ends up at physical address  
\* 0x0000.0000.  
\*  
\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*/  
/\*查看ld script可以发现,isr\_vector段被放置到了flash开始\*/  
.section .isr\_vector,"a",%progbits  
/\*g\_pfnVectors的属性的大小\*/  
.type g\_pfnVectors, %object  
.size g\_pfnVectors, .-g\_pfnVectors

g\_pfnVectors:  
.word \_estack /\*ld script赋值，RAM的结尾地址\*/  
.word Reset\_Handler  
.word NMI\_Handler  
.word HardFault\_Handler  
.word MemManage\_Handler  
.word BusFault\_Handler  
.word UsageFault\_Handler  
.word 0  
.word 0  
.word 0  
.word 0  
.word SVC\_Handler  
.word DebugMon\_Handler  
.word 0  
.word PendSV\_Handler  
.word SysTick\_Handler  
.word WWDG\_IRQHandler  
.word PVD\_IRQHandler  
.word TAMPER\_STAMP\_IRQHandler  
.word RTC\_WKUP\_IRQHandler  
.word FLASH\_IRQHandler  
.word RCC\_IRQHandler  
.word EXTI0\_IRQHandler  
.word EXTI1\_IRQHandler  
.word EXTI2\_IRQHandler  
.word EXTI3\_IRQHandler  
.word EXTI4\_IRQHandler  
.word DMA1\_Channel1\_IRQHandler  
.word DMA1\_Channel2\_IRQHandler  
.word DMA1\_Channel3\_IRQHandler  
.word DMA1\_Channel4\_IRQHandler  
.word DMA1\_Channel5\_IRQHandler  
.word DMA1\_Channel6\_IRQHandler  
.word DMA1\_Channel7\_IRQHandler  
.word ADC1\_IRQHandler  
.word USB\_HP\_IRQHandler  
.word USB\_LP\_IRQHandler  
.word DAC\_IRQHandler  
.word COMP\_IRQHandler  
.word EXTI9\_5\_IRQHandler  
.word LCD\_IRQHandler  
.word TIM9\_IRQHandler  
.word TIM10\_IRQHandler  
.word TIM11\_IRQHandler  
.word TIM2\_IRQHandler  
.word TIM3\_IRQHandler  
.word TIM4\_IRQHandler  
.word I2C1\_EV\_IRQHandler  
.word I2C1\_ER\_IRQHandler  
.word I2C2\_EV\_IRQHandler  
.word I2C2\_ER\_IRQHandler  
.word SPI1\_IRQHandler  
.word SPI2\_IRQHandler  
.word USART1\_IRQHandler  
.word USART2\_IRQHandler  
.word USART3\_IRQHandler  
.word EXTI15\_10\_IRQHandler  
.word RTC\_Alarm\_IRQHandler  
.word USB\_FS\_WKUP\_IRQHandler  
.word TIM6\_IRQHandler  
.word TIM7\_IRQHandler  
.word 0  
.word TIM5\_IRQHandler  
.word SPI3\_IRQHandler  
.word 0  
.word 0  
.word DMA2\_Channel1\_IRQHandler  
.word DMA2\_Channel2\_IRQHandler  
.word DMA2\_Channel3\_IRQHandler  
.word DMA2\_Channel4\_IRQHandler  
.word DMA2\_Channel5\_IRQHandler  
.word 0  
.word COMP\_ACQ\_IRQHandler  
.word 0  
.word 0  
.word 0  
.word 0  
.word 0  
.word BootRAM /\* @0x108. This is for boot in RAM mode for  
STM32L152XC devices. \*/

/\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*  
\*  
\* Provide weak aliases for each Exception handler to the Default\_Handler.  
\* As they are weak aliases, any function with the same name will override  
\* this definition.  
\*  
\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*/

/\*也就是说假如定义了TIM5\_IRQHandler,就等价将新定义的函数的地址赋值给TIM5\_IRQHandler标号\*/  
/\*thumb\_set thumb就是说是thumb入口，因为前面定义的Default\_Handler是Thumb模式的\*/  
/\*set是设置标号的值，就是设置所有的irq服务入口为Default\_Handler\*/  
.weak NMI\_Handler  
.thumb\_set NMI\_Handler,Default\_Handler

.weak HardFault\_Handler  
.thumb\_set HardFault\_Handler,Default\_Handler

.weak MemManage\_Handler  
.thumb\_set MemManage\_Handler,Default\_Handler

.weak BusFault\_Handler  
.thumb\_set BusFault\_Handler,Default\_Handler

.weak UsageFault\_Handler  
.thumb\_set UsageFault\_Handler,Default\_Handler

.weak SVC\_Handler  
.thumb\_set SVC\_Handler,Default\_Handler

.weak DebugMon\_Handler  
.thumb\_set DebugMon\_Handler,Default\_Handler

.weak PendSV\_Handler  
.thumb\_set PendSV\_Handler,Default\_Handler

.weak SysTick\_Handler  
.thumb\_set SysTick\_Handler,Default\_Handler

.weak WWDG\_IRQHandler  
.thumb\_set WWDG\_IRQHandler,Default\_Handler

.weak PVD\_IRQHandler  
.thumb\_set PVD\_IRQHandler,Default\_Handler

.weak TAMPER\_STAMP\_IRQHandler  
.thumb\_set TAMPER\_STAMP\_IRQHandler,Default\_Handler

.weak RTC\_WKUP\_IRQHandler  
.thumb\_set RTC\_WKUP\_IRQHandler,Default\_Handler

.weak FLASH\_IRQHandler  
.thumb\_set FLASH\_IRQHandler,Default\_Handler

.weak RCC\_IRQHandler  
.thumb\_set RCC\_IRQHandler,Default\_Handler

.weak EXTI0\_IRQHandler  
.thumb\_set EXTI0\_IRQHandler,Default\_Handler

.weak EXTI1\_IRQHandler  
.thumb\_set EXTI1\_IRQHandler,Default\_Handler

.weak EXTI2\_IRQHandler  
.thumb\_set EXTI2\_IRQHandler,Default\_Handler

.weak EXTI3\_IRQHandler  
.thumb\_set EXTI3\_IRQHandler,Default\_Handler

.weak EXTI4\_IRQHandler  
.thumb\_set EXTI4\_IRQHandler,Default\_Handler

.weak DMA1\_Channel1\_IRQHandler  
.thumb\_set DMA1\_Channel1\_IRQHandler,Default\_Handler

.weak DMA1\_Channel2\_IRQHandler  
.thumb\_set DMA1\_Channel2\_IRQHandler,Default\_Handler

.weak DMA1\_Channel3\_IRQHandler  
.thumb\_set DMA1\_Channel3\_IRQHandler,Default\_Handler

.weak DMA1\_Channel4\_IRQHandler  
.thumb\_set DMA1\_Channel4\_IRQHandler,Default\_Handler

.weak DMA1\_Channel5\_IRQHandler  
.thumb\_set DMA1\_Channel5\_IRQHandler,Default\_Handler

.weak DMA1\_Channel6\_IRQHandler  
.thumb\_set DMA1\_Channel6\_IRQHandler,Default\_Handler

.weak DMA1\_Channel7\_IRQHandler  
.thumb\_set DMA1\_Channel7\_IRQHandler,Default\_Handler

.weak ADC1\_IRQHandler  
.thumb\_set ADC1\_IRQHandler,Default\_Handler

.weak USB\_HP\_IRQHandler  
.thumb\_set USB\_HP\_IRQHandler,Default\_Handler

.weak USB\_LP\_IRQHandler  
.thumb\_set USB\_LP\_IRQHandler,Default\_Handler

.weak DAC\_IRQHandler  
.thumb\_set DAC\_IRQHandler,Default\_Handler

.weak COMP\_IRQHandler  
.thumb\_set COMP\_IRQHandler,Default\_Handler

.weak EXTI9\_5\_IRQHandler  
.thumb\_set EXTI9\_5\_IRQHandler,Default\_Handler

.weak LCD\_IRQHandler  
.thumb\_set LCD\_IRQHandler,Default\_Handler

.weak TIM9\_IRQHandler  
.thumb\_set TIM9\_IRQHandler,Default\_Handler

.weak TIM10\_IRQHandler  
.thumb\_set TIM10\_IRQHandler,Default\_Handler

.weak TIM11\_IRQHandler  
.thumb\_set TIM11\_IRQHandler,Default\_Handler

.weak TIM2\_IRQHandler  
.thumb\_set TIM2\_IRQHandler,Default\_Handler

.weak TIM3\_IRQHandler  
.thumb\_set TIM3\_IRQHandler,Default\_Handler

.weak TIM4\_IRQHandler  
.thumb\_set TIM4\_IRQHandler,Default\_Handler

.weak I2C1\_EV\_IRQHandler  
.thumb\_set I2C1\_EV\_IRQHandler,Default\_Handler

.weak I2C1\_ER\_IRQHandler  
.thumb\_set I2C1\_ER\_IRQHandler,Default\_Handler

.weak I2C2\_EV\_IRQHandler  
.thumb\_set I2C2\_EV\_IRQHandler,Default\_Handler

.weak I2C2\_ER\_IRQHandler  
.thumb\_set I2C2\_ER\_IRQHandler,Default\_Handler

.weak SPI1\_IRQHandler  
.thumb\_set SPI1\_IRQHandler,Default\_Handler

.weak SPI2\_IRQHandler  
.thumb\_set SPI2\_IRQHandler,Default\_Handler

.weak USART1\_IRQHandler  
.thumb\_set USART1\_IRQHandler,Default\_Handler

.weak USART2\_IRQHandler  
.thumb\_set USART2\_IRQHandler,Default\_Handler

.weak USART3\_IRQHandler  
.thumb\_set USART3\_IRQHandler,Default\_Handler

.weak EXTI15\_10\_IRQHandler  
.thumb\_set EXTI15\_10\_IRQHandler,Default\_Handler

.weak RTC\_Alarm\_IRQHandler  
.thumb\_set RTC\_Alarm\_IRQHandler,Default\_Handler

.weak USB\_FS\_WKUP\_IRQHandler  
.thumb\_set USB\_FS\_WKUP\_IRQHandler,Default\_Handler

.weak TIM6\_IRQHandler  
.thumb\_set TIM6\_IRQHandler,Default\_Handler

.weak TIM7\_IRQHandler  
.thumb\_set TIM7\_IRQHandler,Default\_Handler

.weak TIM5\_IRQHandler  
.thumb\_set TIM5\_IRQHandler,Default\_Handler  
  
.weak SPI3\_IRQHandler  
.thumb\_set SPI3\_IRQHandler,Default\_Handler

.weak DMA2\_Channel1\_IRQHandler  
.thumb\_set DMA2\_Channel1\_IRQHandler,Default\_Handler

.weak DMA2\_Channel2\_IRQHandler  
.thumb\_set DMA2\_Channel2\_IRQHandler,Default\_Handler

.weak DMA2\_Channel3\_IRQHandler  
.thumb\_set DMA2\_Channel3\_IRQHandler,Default\_Handler

.weak DMA2\_Channel4\_IRQHandler  
.thumb\_set DMA2\_Channel4\_IRQHandler,Default\_Handler

.weak DMA2\_Channel5\_IRQHandler  
.thumb\_set DMA2\_Channel5\_IRQHandler,Default\_Handler

.weak COMP\_ACQ\_IRQHandler  
.thumb\_set COMP\_ACQ\_IRQHandler,Default\_Handler

[http_ftp.gnu.org_old-gnu_Manuals_ld-2.9.1_html_mono_ld.html]: http://ftp.gnu.org/old-gnu/Manuals/ld-2.9.1/html_mono/ld.html
[https_sourceware.org_binutils_docs_ld]: https://sourceware.org/binutils/docs/ld/
[http_www.gnu.org_manual]: http://www.gnu.org/manual/